40 SUGAR 



membranous partition a process of diffusion takes place, 

 the denser passing into the lighter, and the lighter 

 into the denser liquid. This occurs in spite of the fact 

 that the membrane is not a filtering medium. It 

 was also found that if the denser liquid contained in 

 solution a mixture of cry st alii zable and uncrystallizable 

 substances, the former would diffuse freely into the 

 lighter liquid, while the uncrystallizable would hardly 

 diffuse at all. This phenomenon was called osmosis, 

 or osmose. The diffusion of the cry st alii zable sub- 

 stances into the lighter liquid was called exosmose, 

 and that of the lighter into the heavier liquid, endos- 

 mose. The easily diffusing substances were called 

 crystalloids, and the others, such as gum, albumen, 

 gelatine or glue (colle) were called colloids. If, therefore, 

 there should be on one side of the membrane a quantity 

 of the juice of the beetroot or the cane, containing 

 crystallizable sugar mingled with many gummy and 

 gelatinous substances, and on the other side water, 

 the solution of sugar would diffuse into the water, and 

 the water into the sugar juice until the liquids on each 

 side of the membrane became of the same density. 

 If the water containing the sugar were then drawn 

 off and fresh water substituted the diffusion would 

 recommence, and this process might be continued until 

 the whole of the sugar had passed away in the form of 

 a nearly pure solution, while the impurities would remain 

 alone in the solution which was originally sugar 

 juice. The membrane may be animal or vegetable 

 parchment paper, for instance, answers the purpose. 



But in nature the walls of the cells of plants form 

 a diffusing medium. The sugar in the beetroot or the 

 cane exists shut up inside the cells. It was found that 

 it could be extracted in the way described above, by 

 diffusion. 



